Known processes for vacuum packaging such photosensitive products comprise, for example, first producing the packaging itself, which may comprise a wrapping sheet folded along its longitudinal axis and welded on both transverse side edges. Then at a feeding station a sheet is inserted into each folded wrapper by applying suction on one side of the wrapper while the other side is maintained by a holding device so as to produce an opening through which sheets may be inserted one at a time in each open folded wrapper. Then the wrappers are sealed in a vacuum sealing apparatus with a small sealing compartment provided with heat-sealing bars for sealing the open edges of each folded wrapper. With such an apparatus, each wrapper must be brought into the sealing compartment; a valve must be opened to create the vacuum immediately; the heating bars must be put into action to heat the open edges of the wrapper so that the adhesive layer melts and the longitudinal open edge is sealed; the valve must be opened to return to atmospheric pressure and the compartment must be opened. All these operations take time, are difficult to monitor and do not allow high speed series packaging. In addition, it is often long and difficult to adapt the system to other packaging sizes.
German Patent No. 1,511,628 describes a vacuum packaging process and apparatus in which a partial vacuum is applied after the web of packaging material has been formed into a longitudinally extending tube and sealed along its longitudinal edge and across one transverse edge. Because the package is partially formed before the product is inserted and the vacuum then applied, the jet around the product could be irregular. A similar process and apparatus are disclosed in U.S. Pat. No. 4,177,622.